As described in Patent Document 1, conventional induction heating cooking devices have been provided with a plurality of electrodes around outer peripheries of heating coils and have been adapted to perform boiling-over detection based on the changes of the capacitances of these electrodes.
FIG. 5 is a view illustrating the structure of a conventional induction heating cooking device described in Patent Document 1. FIG. 6 is a graph illustrating a capacitance change in an electrode for performing boiling-over detection, in the induction heating cooking device described in Patent Document 1. As illustrated in FIG. 5, in the conventional induction heating cooking device, a plurality of electrodes 103 each having a small disk shape are placed and dispersed in a concentric shape around the outer periphery of a heating coil 104. The respective electrodes 103 which are placed and dispersed are connected to a capacitance determination circuit 106, for detecting the capacitances between the respective electrodes 103 and dielectric members around the electrodes, such as air or heating containers.
As described above, in the conventional induction heating cooking device, the plurality of the electrodes 103 are placed and dispersed around the outer periphery of the heating coil 104. Therefore, in the event of boiling over of liquid from the peripheral edge portion of a heating container such as a pan placed above the heating coil 104 with a top board (top plate) interposed, the liquid having boiled over exists on or around any of the electrodes 103. As a result, the liquid having boiled over changes the capacitance of any of the electrodes 103, thereby causing the boiling over to be detected.
In the state where no boiling over has occurred during heating of the heating container, air having a relative dielectric constant of “1” mainly exists between the electrodes 103 and the heating container, in addition to the top board. However, if boiling over occurs, water is interposed between the electrodes 103 and the heating container, which induces abrupt increases of the capacitances. Accordingly, by detecting the changes of the capacitances of the electrodes 103 as described above, it is possible to detect boiling over.
In the induction heating cooking device described in Patent Document 1, when an abrupt increase in the capacitances of the electrodes 103 is detected (see FIG. 6), a control circuit 105 determines that boiling over has occurred. At this time, the induction heating cooking device described in Patent Document 1 is adapted to stop the operation of a driving circuit 102 or to reduce the electric current flowing through the heating coil 104, wherein the driving circuit 102 is adapted to produce high-frequency electric power when electric power from an AC power supply 101 is inputted thereto.    Patent Document 1: JP 2008-159494 A